Heat treatment method for heating substrate by irradiating substrate with flash of light

ABSTRACT

A flash heating part in a heat treatment apparatus includes 30 built-in flash lamps, and irradiates a semiconductor wafer held by a holder in a chamber with a flash of light. Thirty switching elements are provided in a one-to-one correspondence with the 30 flash lamps. Each of the switching elements defines the waveform of current flowing through a corresponding one of the flash lamps by intermittently supplying electrical charge thereto. Radiation thermometers measure an in-plane temperature distribution of the semiconductor wafer during flash irradiation. Based on the results of measurement with the radiation thermometers, a controller individually controls the operations of the 30 switching elements to individually define the light emission patterns of the 30 flash lamps.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 14/142,991,filed Dec. 30, 2013 in the name of Hiroki KIYAMA and entitled HEATTREATMENT APPARATUS AND HEAT TREATMENT METHOD FOR HEATING SUBSTRATE BYIRRADIATING SUBSTRATE WITH FLASH OF LIGHT, which claims priority fromJapanese Application No. 2013-010836, filed Jan. 24, 2013.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a heat treatment apparatus and a heattreatment method for heating a thin plate-like precision electronicsubstrate such as a semiconductor wafer and a glass substrate for aliquid crystal display device (hereinafter referred to simply as a“substrate”) by irradiating the substrate with a flash of light.

Description of the Background Art

In the process of manufacturing a semiconductor device, impurity dopingis an essential step for forming a pn junction in a semiconductor wafer.At present, it is common practice to perform impurity doping by an ionimplantation process and a subsequent annealing process. The ionimplantation process is a technique for causing ions of impurityelements such as boron (B), arsenic (As) and phosphorus (P) to collideagainst the semiconductor wafer of silicon with high accelerationvoltage, thereby physically implanting the impurities into thesemiconductor wafer. The implanted impurities are activated by thesubsequent annealing process. When annealing time in this annealingprocess is approximately several seconds or longer, the implantedimpurities are deeply diffused by heat. This results in a junction depthmuch greater than a required depth, which might constitute a hindranceto good device formation.

In recent years, attention has been given to flash lamp annealing (FLA)that is an annealing technique for heating a semiconductor wafer in anextremely short time. The flash lamp annealing is a heat treatmenttechnique in which xenon flash lamps (the term “flash lamp” as usedhereinafter refers to a “xenon flash lamp”) are used to irradiate asurface of a semiconductor wafer with a flash of light, thereby raisingthe temperature of only the surface of the semiconductor wafer implantedwith impurities in an extremely short time (several milliseconds orless).

The xenon flash lamps have a spectral distribution of radiation rangingfrom ultraviolet to near-infrared regions. The wavelength of lightemitted from the xenon flash lamps is shorter than that of light emittedfrom conventional halogen lamps, and approximately coincides with afundamental absorption band of a silicon semiconductor wafer. Thus, whena semiconductor wafer is irradiated with a flash of light emitted fromthe xenon flash lamps, the temperature of the semiconductor wafer can beraised rapidly, with only a small amount of light transmitted throughthe semiconductor wafer. Also, it has turned out that flash irradiation,that is, the irradiation of a semiconductor wafer with a flash of lightin an extremely short time of several milliseconds or less allows aselective temperature rise only near the surface of the semiconductorwafer. Therefore, the temperature rise in an extremely short time withthe xenon flash lamps allows only the activation of impurities to beachieved without deep diffusion of the impurities.

Heat treatment apparatuses which employ such xenon flash lamps aredisclosed in U.S. Patent Application Publication Nos. 2009/0067823 and2009/0103906 in which an insulated gate bipolar transistor (IGBT) isconnected to a light emitting circuit for a flash lamp to control thelight emission from the flash lamp. In the apparatuses disclosed in U.S.Patent Application Publication Nos. 2009/0067823 and 2009/0103906, apredetermined pulse signal is outputted to the gate of the IGBT todefine the waveform of current flowing through the flash lamp, therebycontrolling the light emission from the lamp. This achieves theadjustment of the temperature profile of the front surface of asemiconductor wafer.

In the apparatuses disclosed in U.S. Patent Application Publication Nos.2009/0067823 and 2009/0103906, 30 IGBTs are provided in a one-to-onecorrespondence with 30 flash lamps, and a common pulse signal isoutputted to the 30 IGBTs. Thus, currents having the same waveform flowthrough the 30 flash lamps, so that the 30 flash lamps emit light in asimilar fashion.

Even if a plurality of flash lamps emit light in a similar fashion, anactual flash lamp annealer has a problem such that nonuniformity inilluminance coming from an apparatus configuration problem results inthe nonuniform in-plane temperature distribution of a semiconductorwafer during flash irradiation. In general, a semiconductor wafer Wshows a tendency to be lower in temperature in a peripheral portionthereof than near a central portion thereof.

SUMMARY OF THE INVENTION

The present invention is intended for a heat treatment apparatus forheating a substrate by irradiating the substrate with a flash of light.

According to one aspect of the present invention, the heat treatmentapparatus comprises: a chamber for receiving a substrate therein; aholder for holding the substrate in the chamber; a plurality of flashlamps for irradiating the substrate held by the holder with a flash oflight; a plurality of switching elements provided in a one-to-onecorrespondence with the flash lamps and each defining the waveform ofcurrent flowing through a corresponding one of the flash lamps; and alight emission controller for individually controlling the operations ofthe switching elements to individually define the light emissionpatterns of the flash lamps.

The heat treatment apparatus causes the illuminance of flash lampscorresponding to a region where illuminance is insufficient to becomerelatively high, thereby achieving the uniform in-plane temperaturedistribution of the substrate during flash irradiation.

Preferably, the heat treatment apparatus further comprises a pluralityof temperature sensors for measuring the temperatures of differentregions, respectively, of a front surface of the substrate held by theholder, and the light emission controller controls the operations of theswitching elements, based on results of measurement with the temperaturesensors.

The heat treatment apparatus causes the illuminance of a flash of lightin a region of the substrate where a temperature decrease occurs tobecome relatively high, thereby achieving the uniform in-planetemperature distribution of the substrate during flash irradiation.

Preferably, the heat treatment apparatus further comprises a pluralityof illuminance sensors for measuring the illuminances of differentregions, respectively, of the arrangement of the flash lamps, and thelight emission controller controls the operations of the switchingelements, based on results of measurement with the illuminance sensors.

The heat treatment apparatus causes the illuminance of a flash of lightfrom a region of the arrangement where illuminance is low to becomerelatively high, thereby achieving the uniform in-plane temperaturedistribution of the substrate during flash irradiation.

The present invention is also intended for a method of heating asubstrate by irradiating the substrate with a flash of light.

According to one aspect of the present invention, the method comprisesthe step of individually controlling the operations of a plurality ofswitching elements provided in a one-to-one correspondence with aplurality of flash lamps for emitting a flash of light and each definingthe waveform of current flowing through a corresponding one of the flashlamps, to individually define the light emission patterns of the flashlamps.

The method causes the illuminance of flash lamps corresponding to aregion where illuminance is insufficient to become relatively high,thereby achieving the uniform in-plane temperature distribution of thesubstrate during flash irradiation.

Preferably, the operations of the switching elements are controlled,based on results of measurement of temperatures of different regions,respectively, of a front surface of a substrate irradiated with a flashof light.

The method causes the illuminance of a flash of light in a region of thesubstrate where a temperature decrease occurs to become relatively high,thereby achieving the uniform in-plane temperature distribution of thesubstrate during flash irradiation.

Preferably, the operations of the switching elements are controlled,based on results of measurement of illuminances of different regions,respectively, of the arrangement of the flash lamps.

The method causes the illuminance of a flash of light from a region ofthe arrangement where illuminance is low to become relatively high,thereby achieving the uniform in-plane temperature distribution of thesubstrate during flash irradiation.

It is therefore an object of the present invention to achieve a uniformin-plane temperature distribution of a substrate during flashirradiation.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing a configuration of aheat treatment apparatus according to the present invention;

FIG. 2 is a perspective view showing the entire external appearance of aholder;

FIG. 3 is a top plan view of the holder;

FIG. 4 is a side view of the holder as seen from one side;

FIG. 5 is a plan view of a transfer mechanism;

FIG. 6 is a side view of the transfer mechanism;

FIG. 7 is a plan view showing an arrangement of halogen lamps;

FIG. 8 is a diagram showing a light emitting circuit for a flash lamp;

FIG. 9 is a graph showing changes in the temperature of the frontsurface of a semiconductor wafer;

FIG. 10 is a graph showing an example of the waveform of current flowingthrough flash lamps;

FIG. 11 is a graph showing changes in the temperature of the frontsurface of a semiconductor wafer when the current having the waveform ofFIG. 10 flows through the flash lamps;

FIG. 12 is a graph showing another example of the waveform of currentflowing through the flash lamps;

FIG. 13 is a graph showing changes in the temperature of the frontsurface of a semiconductor wafer when the current having the waveform ofFIG. 12 flows through the flash lamps; and

FIG. 14 is a view showing an example of the flash lamps divided into aplurality of flash lamp groups.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention will now bedescribed in detail with reference to the drawings. In FIG. 1 and thesubsequent figures, the dimensions of components and the number ofcomponents are shown in exaggeration or in simplified form, asappropriate, for the sake of easier understanding.

First Preferred Embodiment

FIG. 1 is a longitudinal sectional view showing a configuration of aheat treatment apparatus 1 according to the present invention. The heattreatment apparatus 1 according to a first preferred embodiment of thepresent invention is a flash lamp annealer for irradiating a disk-shapedsemiconductor wafer W serving as a substrate with a flash of light toheat the semiconductor wafer W. The size of the semiconductor wafer W tobe treated is not particularly limited. For example, the semiconductorwafer W to be treated has a diameter of 300 mm and 450 mm. Thesemiconductor wafer W prior to the transport into the heat treatmentapparatus 1 is implanted with impurities. The heat treatment apparatus 1performs a heating treatment on the semiconductor wafer W to therebyactivate the impurities implanted in the semiconductor wafer W.

The heat treatment apparatus 1 includes a chamber 6 for receiving asemiconductor wafer W therein, a flash heating part 5 including aplurality of built-in flash lamps FL, and a halogen heating part 4including a plurality of built-in halogen lamps HL. The flash heatingpart 5 is provided over the chamber 6, and the halogen heating part 4 isprovided under the chamber 6. The heat treatment apparatus 1 furtherincludes a holder 7 provided inside the chamber 6 and for holding asemiconductor wafer W in a horizontal attitude, and a transfer mechanism10 provided inside the chamber 6 and for transferring a semiconductorwafer W between the holder 7 and the outside of the heat treatmentapparatus 1. The heat treatment apparatus 1 further includes acontroller 3 for controlling operating mechanisms provided in thehalogen heating part 4, the flash heating part 5, and the chamber 6 tocause the operating mechanisms to heat-treat a semiconductor wafer W.

The chamber 6 is configured such that upper and lower chamber windows 63and 64 made of quartz are mounted to the top and bottom, respectively,of a tubular chamber side portion 61. The chamber side portion 61 has agenerally tubular shape having an open top and an open bottom. The upperchamber window 63 is mounted to block the top opening of the chamberside portion 61, and the lower chamber window 64 is mounted to block thebottom opening thereof. The upper chamber window 63 forming the ceilingof the chamber 6 is a disk-shaped member made of quartz, and serves as aquartz window that transmits flashes of light emitted from the flashheating part 5 therethrough into the chamber 6. The lower chamber window64 forming the floor of the chamber 6 is also a disk-shaped member madeof quartz, and serves as a quartz window that transmits light emittedfrom the halogen heating part 4 therethrough into the chamber 6.

An upper reflective ring 68 is mounted to an upper portion of the innerwall surface of the chamber side portion 61, and a lower reflective ring69 is mounted to a lower portion thereof. Both of the upper and lowerreflective rings 68 and 69 are in the form of an annular ring. The upperreflective ring 68 is mounted by being inserted downwardly from the topof the chamber side portion 61. The lower reflective ring 69, on theother hand, is mounted by being inserted upwardly from the bottom of thechamber side portion 61 and fastened with screws not shown. In otherwords, the upper and lower reflective rings 68 and 69 are removablymounted to the chamber side portion 61. An interior space of the chamber6, i.e. a space surrounded by the upper chamber window 63, the lowerchamber window 64, the chamber side portion 61, and the upper and lowerreflective rings 68 and 69, is defined as a heat treatment space 65.

A recessed portion 62 is defined in the inner wall surface of thechamber 6 by mounting the upper and lower reflective rings 68 and 69 tothe chamber side portion 61. Specifically, the recessed portion 62 isdefined which is surrounded by a middle portion of the inner wallsurface of the chamber side portion 61 where the reflective rings 68 and69 are not mounted, a lower end surface of the upper reflective ring 68,and an upper end surface of the lower reflective ring 69. The recessedportion 62 is provided in the form of a horizontal annular ring in theinner wall surface of the chamber 6, and surrounds the holder 7 whichholds a semiconductor wafer W.

The chamber side portion 61, and the upper and lower reflective rings 68and 69 are made of a metal material (e.g., stainless steel) with highstrength and high heat resistance. The inner peripheral surfaces of theupper and lower reflective rings 68 and 69 are provided as mirrorsurfaces by electrolytic nickel plating.

The chamber side portion 61 is provided with a transport opening(throat) 66 for the transport of a semiconductor wafer W therethroughinto and out of the chamber 6. The transport opening 66 is openable andclosable by a gate valve 185. The transport opening 66 is connected incommunication with an outer peripheral surface of the recessed portion62. Thus, when the transport opening 66 is opened by the gate valve 185,a semiconductor wafer W is allowed to be transported through thetransport opening 66 and the recessed portion 62 into and out of theheat treatment space 65. When the transport opening 66 is closed by thegate valve 185, the heat treatment space 65 in the chamber 6 is anenclosed space.

At least one gas supply opening 81 for supplying a treatment gas (inthis preferred embodiment, nitrogen (N₂) gas) therethrough into the heattreatment space 65 is provided in an upper portion of the inner wall ofthe chamber 6. The gas supply opening 81 is provided above the recessedportion 62, and may be provided in the upper reflective ring 68. The gassupply opening 81 is connected in communication with a gas supply pipe83 through a buffer space 82 provided in the form of an annular ringinside the side wall of the chamber 6. The gas supply pipe 83 isconnected to a nitrogen gas supply source 85. A valve 84 is inserted atsome midpoint in the gas supply pipe 83. When the valve 84 is opened,nitrogen gas is fed from the nitrogen gas supply source 85 to the bufferspace 82. The nitrogen gas flowing in the buffer space 82 flows in aspreading manner within the buffer space 82 which is lower in fluidresistance than the gas supply opening 81, and is supplied through thegas supply opening 81 into the heat treatment space 65.

On the other hand, at least one gas exhaust opening 86 for exhausting agas from the heat treatment space 65 is provided in a lower portion ofthe inner wall of the chamber 6. The gas exhaust opening 86 is providedbelow the recessed portion 62, and may be provided in the lowerreflective ring 69. The gas exhaust opening 86 is connected incommunication with a gas exhaust pipe 88 through a buffer space 87provided in the form of an annular ring inside the side wall of thechamber 6. The gas exhaust pipe 88 is connected to an exhaust part 190.A valve 89 is inserted at some midpoint in the gas exhaust pipe 88. Whenthe valve 89 is opened, the gas in the heat treatment space 65 isexhausted through the gas exhaust opening 86 and the buffer space 87 tothe gas exhaust pipe 88. The at least one gas supply opening 81 and theat least one gas exhaust opening 86 may include a plurality of gassupply openings 81 and a plurality of gas exhaust openings 86,respectively, arranged in a circumferential direction of the chamber 6,and may be in the form of slits. The nitrogen gas supply source 85 andthe exhaust part 190 may be mechanisms provided in the heat treatmentapparatus 1 or be utility systems in a factory in which the heattreatment apparatus 1 is installed.

A gas exhaust pipe 191 for exhausting the gas from the heat treatmentspace 65 is also connected to a distal end of the transport opening 66.The gas exhaust pipe 191 is connected through a valve 192 to the exhaustpart 190. By opening the valve 192, the gas in the chamber 6 isexhausted through the transport opening 66.

FIG. 2 is a perspective view showing the entire external appearance ofthe holder 7. FIG. 3 is a top plan view of the holder 7. FIG. 4 is aside view of the holder 7 as seen from one side. The holder 7 includes abase ring 71, coupling portions 72, and a susceptor 74. The base ring71, the coupling portions 72, and the susceptor 74 are all made ofquartz. In other words, the whole of the holder 7 is made of quartz.

The base ring 71 is a quartz member in the form of an annular ring. Thebase ring 71 is supported by the wall surface of the chamber 6 by beingplaced on the bottom surface of the recessed portion 62 (with referenceto FIG. 1). The multiple coupling portions 72 (in the present preferredembodiment, four coupling portions 72) are mounted upright on the uppersurface of the base ring 71 in the form of the annular ring and arrangedin a circumferential direction of the base ring 71. The couplingportions 72 are quartz members, and are rigidly secured to the base ring71 by welding. The base ring 71 may be of an arcuate shape such that aportion is removed from the annular ring.

The susceptor 74 having a planar shape is supported by the four couplingportions 72 provided on the base ring 71. The susceptor 74 is agenerally circular planar member made of quartz. The diameter of thesusceptor 74 is greater than that of a semiconductor wafer W. In otherwords, the susceptor 74 has a size, as seen in plan view, greater thanthat of the semiconductor wafer W. Multiple (in the present preferredembodiment, five) guide pins 76 are mounted upright on the upper surfaceof the susceptor 74. The five guide pins 76 are disposed along thecircumference of a circle concentric with the outer circumference of thesusceptor 74. The diameter of a circle on which the five guide pins 76are disposed is slightly greater than the diameter of the semiconductorwafer W. The guide pins 76 are also made of quartz. The guide pins 76may be machined from a quartz ingot integrally with the susceptor 74.Alternatively, the guide pins 76 separately machined may be attached tothe susceptor 74 by welding and the like.

The four coupling portions 72 provided upright on the base ring 71 andthe lower surface of a peripheral portion of the susceptor 74 arerigidly secured to each other by welding. In other words, the susceptor74 and the base ring 71 are fixedly coupled to each other with thecoupling portions 72, and the holder 7 is an integrally formed membermade of quartz. The base ring 71 of such a holder 7 is supported by thewall surface of the chamber 6, whereby the holder 7 is mounted to thechamber 6. With the holder 7 mounted to the chamber 6, the susceptor 74of a generally disc-shaped configuration assumes a horizontal attitude(an attitude such that the normal to the susceptor 74 coincides with avertical direction). A semiconductor wafer W transported into thechamber 6 is placed and held in a horizontal attitude on the susceptor74 of the holder 7 mounted to the chamber 6. The semiconductor wafer Wis placed inside the circle defined by the five guide pins 76. Thisprevents the horizontal misregistration of the semiconductor wafer W.The number of guide pins 76 is not limited to five, but may bedetermined so as to prevent the misregistration of the semiconductorwafer W.

As shown in FIGS. 2 and 3, an opening 78 and a notch 77 are provided inthe susceptor 74 so as to extend vertically through the susceptor 74.The notch 77 is provided to allow a distal end portion of a probe of acontact-type thermometer 130 including a thermocouple to passtherethrough. The opening 78, on the other hand, is provided for aradiation thermometer 120 to receive radiation (infrared radiation)emitted from the lower surface of the semiconductor wafer W held by thesusceptor 74. The susceptor 74 further includes four through holes 79bored therein and designed so that lift pins 12 of the transfermechanism 10 to be described later pass through the through holes 79,respectively, to transfer a semiconductor wafer W.

FIG. 5 is a plan view of the transfer mechanism 10. FIG. 6 is a sideview of the transfer mechanism 10. The transfer mechanism 10 includes apair of transfer arms 11. The transfer arms 11 are of an arcuateconfiguration extending substantially along the annular recessed portion62. Each of the transfer arms 11 includes the two lift pins 12 mountedupright thereon. The transfer arms 11 are pivotable by a horizontalmovement mechanism 13. The horizontal movement mechanism 13 moves thepair of transfer arms 11 horizontally between a transfer operationposition (a position indicated by solid lines in FIG. 5) in which asemiconductor wafer W is transferred to and from the holder 7 and aretracted position (a position indicated by dash-double-dot lines inFIG. 5) in which the transfer arms 11 do not overlap the semiconductorwafer W held by the holder 7 as seen in plan view. The horizontalmovement mechanism 13 may be of the type which causes individual motorsto pivot the transfer arms 11 respectively or of the type which uses alinkage mechanism to cause a single motor to pivot the pair of transferarms 11 in cooperative relation.

The transfer arms 11 are moved upwardly and downwardly together with thehorizontal movement mechanism 13 by an elevating mechanism 14. As theelevating mechanism 14 moves up the pair of transfer arms 11 in theirtransfer operation position, the four lift pins 12 in total pass throughthe respective four through holes 79 (with reference to FIGS. 2 and 3)bored in the susceptor 74 so that the upper ends of the lift pins 12protrude from the upper surface of the susceptor 74. On the other hand,as the elevating mechanism 14 moves down the pair of transfer arms 11 intheir transfer operation position to take the lift pins 12 out of therespective through holes 79 and the horizontal movement mechanism 13moves the pair of transfer arms 11 so as to open the transfer arms 11,the transfer arms 11 move to their retracted position. The retractedposition of the pair of transfer arms 11 is immediately over the basering 71 of the holder 7. The retracted position of the transfer arms 11is inside the recessed portion 62 because the base ring 71 is placed onthe bottom surface of the recessed portion 62. An exhaust mechanism notshown is also provided near the location where the drivers (thehorizontal movement mechanism 13 and the elevating mechanism 14) of thetransfer mechanism 10 are provided, and is configured to exhaust anatmosphere around the drivers of the transfer mechanism 10 to theoutside of the chamber 6.

Referring again to FIG. 1, two radiation thermometers 140 and 150 areprovided inside the chamber 6. While the radiation thermometer 120described above (FIG. 2) measures the temperature of the lower surfaceof the semiconductor wafer W, the radiation thermometers 140 and 150 aretemperature sensors for measuring the temperature of the upper surfaceof the semiconductor wafer W. The radiation thermometers 140 and 150 areprovided above the susceptor 74 of the holder 7. The radiationthermometers 140 and 150 are also provided obliquely above thesemiconductor wafer W held by the holder 7 so as not to be obstacles tothe flash irradiation from the flash lamps FL. The radiationthermometers 140 and 150 may be provided inside the recessed portion 62.

Each of the radiation thermometers 140 and 150 includes a fast-responseinfrared photodetection element. The wavelength range measured by theinfrared photodetection elements of the radiation thermometers 140 and150 is preferably a wavelength range to which the material (in thispreferred embodiment, quartz) of the upper chamber window 63 and thelower chamber window 64 is not pervious. The radiation thermometers 140and 150 receive infrared radiation emitted from the upper surface of thesemiconductor wafer W held by the holder 7 to measure the temperature ofthe upper surface of the wafer W, based on the intensity (the amount ofenergy) of the infrared radiation.

The radiation thermometer 140 and the radiation thermometer 150 aredifferent from each other in temperature measurement region on the uppersurface of the semiconductor wafer W. The radiation thermometer 140detects infrared radiation emitted from a peripheral portion of thesemiconductor wafer W held by the holder 7 to measure the temperature ofthe peripheral portion. The radiation thermometer 150, on the otherhand, detects infrared radiation emitted from the vicinity of a centralportion of the semiconductor wafer W held by the holder 7 to measure thetemperature of the vicinity of the central portion. The number ofradiation thermometers which measure the temperature of the uppersurface of the semiconductor wafer W is not limited to two, but may bethree or more. For example, another radiation thermometer for measuringthe temperature of an intermediate region between the peripheral portionand the central portion of the semiconductor wafer W may be provided inaddition to the radiation thermometers 140 and 150. Alternatively,another radiation thermometer may be provided which measures thetemperature of a peripheral portion of the semiconductor wafer Wdifferent from the peripheral portion whose temperature is measured bythe radiation thermometer 140. It is only necessary that at least tworadiation thermometers which measure the temperatures of differentregions of the upper surface of the semiconductor wafer W held by theholder 7 are provided.

The flash heating part 5 provided over the chamber 6 includes anenclosure 51, a light source provided inside the enclosure 51 andincluding the multiple (in the present preferred embodiment, 30) xenonflash lamps FL, and a reflector 52 provided inside the enclosure 51 soas to cover the light source from above. The flash heating part 5further includes a lamp light radiation window 53 mounted to the bottomof the enclosure 51. The lamp light radiation window 53 forming thefloor of the flash heating part 5 is a plate-like quartz window made ofquartz. The flash heating part 5 is provided over the chamber 6, wherebythe lamp light radiation window 53 is opposed to the upper chamberwindow 63. The flash lamps FL direct a flash of light from over thechamber 6 through the lamp light radiation window 53 and the upperchamber window 63 toward the heat treatment space 65.

The flash lamps FL, each of which is a rod-shaped lamp having anelongated cylindrical shape, are arranged in a plane so that thelongitudinal directions of the respective flash lamps FL are in parallelwith each other along the main surface of a semiconductor wafer W heldby the holder 7 (that is, in a horizontal direction). Thus, a planedefined by the arrangement of the flash lamps FL is also a horizontalplane.

FIG. 8 is a diagram showing a light emitting circuit for each flash lampFL. As shown in FIG. 8, a capacitor 93, a coil 94, and a switchingelement 96 are connected in series with a flash lamp FL. An example ofthe switching element 96 used herein includes an IGBT (insulated-gatebipolar transistor). Also as shown in FIG. 8, the controller 3 includesa pulse generator 31 and a waveform setting part 32, and is connected toan input part 33. Examples of the input part 33 used herein includevarious known input devices such as a keyboard, a mouse, and a touchpanel. The waveform setting part 32 sets the waveform of a pulse signal,based on an input from the input part 33 or a computation processingresult of the controller 3. The pulse generator 31 generates the pulsesignal in accordance with the waveform sets by the waveform setting part32.

The flash lamp FL includes a rod-shaped glass tube (discharge tube) 92containing xenon gas sealed therein and having positive and negativeelectrodes provided on opposite ends thereof, and a trigger electrode 91attached to the outer peripheral surface of the glass tube 92. A triggercircuit 97 is capable of applying a high voltage to the triggerelectrode 91. The timing of the voltage application from the triggercircuit 97 to the trigger electrode 91 is controlled by the controller3.

In the light emitting circuit for the flash lamps FL, a charging unit(charging part) 95 is connected in parallel with the capacitor 93. Thecharging unit 95 applies a predetermined voltage to the capacitor 93, sothat the capacitor 93 is charged in accordance with the applied voltage(charging voltage). The charging voltage applied from the charging unit95 to the capacitor 93 is controlled by the controller 3.

The IGBT used as the switching element 96 is a bipolar transistor whichincludes a MOSFET (metal-oxide-semiconductor field-effect transistor)incorporated in the gate thereof, and is suitable for handling a largeamount of power. The pulse generator 31 in the controller 3 applies thepulse signal to the gate of the IGBT serving as the switching element96. When a voltage (“high” voltage) not less than a predetermined levelis applied to the gate of the switching element 96, the switchingelement 96 turns on. When a voltage (“low” voltage) less than thepredetermined level is applied to the gate of the switching element 96,the switching element 96 turns off. In this manner, the light emittingcircuit including the flash lamp FL is turned on and off by theswitching element 96. By turning the switching element 96 on and off, aconnection between the flash lamp FL and the capacitor 93 correspondingthereto is made and broken.

Even if, with the capacitor 93 in the charged state, the switchingelement 96 turns on to apply a high voltage across the electrodes of theglass tube 92, no electricity will flow through the glass tube 92 in anormal state because the xenon gas is electrically insulative. However,when the trigger circuit 97 applies a high voltage to the triggerelectrode 91 to produce an electrical breakdown, an electrical dischargebetween the electrodes causes a current to flow momentarily in the glasstube 92, so that xenon atoms or molecules are excited at this time tocause light emission.

The light emitting circuit shown in FIG. 8 is provided for each of the30 flash lamps FL. That is, 30 switching elements 96, 30 capacitors 93and 30 coils 94 are provided in a one-to-one correspondence with the 30flash lamps. Also, 30 charging units 95 are provided in a one-to-onecorrespondence with the 30 capacitors 93.

Also, the reflector 52 shown in FIG. 1 is provided over the plurality offlash lamps FL so as to cover all of the flash lamps FL. A fundamentalfunction of the reflector 52 is to reflect the light emitted from theplurality of flash lamps FL toward the holder 7. The reflector 52 is aplate made of an aluminum alloy. A surface of the reflector 52 (asurface which faces the flash lamps FL) is roughened by abrasiveblasting. Two illuminance sensors 240 and 250 are provided on an uppersurface (a surface opposite from the flash lamps FL) of the reflector52. Small holes are formed in parts of the reflector 52 where theilluminance sensors 240 and 250 are provided. The illuminance sensors240 and 250 receive light emitted from the flash lamps FL through thesmall holes of the reflector 52. Each of the illuminance sensors 240 and250 includes a fast-response photodiode, for example, to measure theilluminance of light emitted from the flash lamps FL.

The illuminance sensor 240 and the illuminance sensor 250 are differentfrom each other in illuminance measurement region in the arrangement ofthe 30 flash lamps FL. The illuminance sensor 240 is provided over thevicinity of an edge portion of the arrangement of the 30 flash lamps FLto measure the illuminance of flashes of light in the vicinity of theedge portion. The illuminance sensor 250, on the other hand, is providedover the vicinity of a central portion of the arrangement of the 30flash lamps FL to measure the illuminance of flashes of light in thevicinity of the central portion. The number of illuminance sensors isnot limited to two, but may be three or more. For example, anotherilluminance sensor for measuring the illuminance in an intermediateregion between the edge portion and the central portion of thearrangement of the 30 flash lamps FL may be provided in addition to theilluminance sensors 240 and 250. It is only necessary that at least twoilluminance sensors which measure the illuminance in different regionsof the arrangement of the 30 flash lamps FL are provided.

The multiple (in the present preferred embodiment, 40) halogen lamps HLare incorporated in the halogen heating part 4 provided under thechamber 6. The halogen lamps HL direct light from under the chamber 6through the lower chamber window 64 toward the heat treatment space 65.FIG. 7 is a plan view showing an arrangement of the multiple halogenlamps HL. In the present preferred embodiment, 20 halogen lamps HL arearranged in an upper tier, and 20 halogen lamps HL are arranged in alower tier. Each of the halogen lamps HL is a rod-shaped lamp having anelongated cylindrical shape. The 20 halogen lamps HL in each of theupper and lower tiers are arranged so that the longitudinal directionsthereof are in parallel with each other along a main surface of asemiconductor wafer W held by the holder 7 (that is, in a horizontaldirection). Thus, a plane defined by the arrangement of the halogenlamps HL in each of the upper and lower tiers is also a horizontalplane.

As shown in FIG. 7, the halogen lamps HL in each of the upper and lowertiers are disposed at a higher density in a region opposed to theperipheral portion of the semiconductor wafer W held by the holder 7than in a region opposed to the central portion thereof. In other words,the halogen lamps HL in each of the upper and lower tiers are arrangedat shorter intervals in the edge portion of the lamp arrangement than inthe central portion thereof. This allows a greater amount of light toimpinge upon the peripheral portion of the semiconductor wafer W where atemperature decrease is prone to occur when the semiconductor wafer W isheated by the irradiation thereof with light from the halogen heatingpart 4.

The group of halogen lamps HL in the upper tier and the group of halogenlamps HL in the lower tier are arranged to intersect each other in alattice pattern. In other words, the 40 halogen lamps HL in total aredisposed so that the longitudinal direction of the halogen lamps HL inthe upper tier and the longitudinal direction of the halogen lamps HL inthe lower tier are orthogonal to each other.

Each of the halogen lamps HL is a filament-type light source whichpasses current through a filament disposed in a glass tube to make thefilament incandescent, thereby emitting light. A gas prepared byintroducing a halogen element (iodine, bromine and the like) in traceamounts into an inert gas such as nitrogen, argon and the like is sealedin the glass tube. The introduction of the halogen element allows thetemperature of the filament to be set at a high temperature whilesuppressing a break in the filament. Thus, the halogen lamps HL have theproperties of having a longer life than typical incandescent lamps andbeing capable of continuously emitting intense light. In addition, thehalogen lamps HL, which are rod-shaped lamps, have a long life. Thearrangement of the halogen lamps HL in a horizontal direction providesgood efficiency of radiation toward the semiconductor wafer W providedover the halogen lamps HL.

The controller 3 controls the aforementioned various operatingmechanisms provided in the heat treatment apparatus 1. The controller 3is similar in hardware configuration to a typical computer.Specifically, the controller 3 includes a CPU for performing variouscomputation processes, a ROM or read-only memory for storing a basicprogram therein, a RAM or readable/writable memory for storing variouspieces of information therein, and a magnetic disk for storing controlsoftware, data and the like therein. The CPU in the controller 3executes a predetermined processing program, whereby the processes inthe heat treatment apparatus 1 proceed. Also, as shown in FIG. 8, thecontroller 3 includes the pulse generator 31 and the waveform settingpart 32. As mentioned earlier, the waveform setting part 32 of thecontroller 3 sets the waveform of the pulse signal, and the pulsegenerator 31 outputs the pulse signal to the gate of the switchingelement 96 in accordance with the waveform. Further, the controller 3controls the charging voltage applied from the charging unit 95 to thecapacitor 93.

The heat treatment apparatus 1 further includes, in addition to theaforementioned components, various cooling structures to prevent anexcessive temperature rise in the halogen heating part 4, the flashheating part 5 and the chamber 6 because of the heat energy generatedfrom the halogen lamps HL and the flash lamps FL during the heattreatment of a semiconductor wafer W. As an example, a water coolingtube (not shown) is provided in the walls of the chamber 6. Also, thehalogen heating part 4 and the flash heating part 5 have an air coolingstructure for forming a gas flow therein to exhaust heat. Air issupplied to a gap between the upper chamber window 63 and the lamp lightradiation window 53 to cool down the flash heating part 5 and the upperchamber window 63.

Next, a procedure for the treatment of a semiconductor wafer W in theheat treatment apparatus 1 will be described. A semiconductor wafer W tobe treated herein is a semiconductor substrate of silicon in whichimpurities (ions) are introduced by an ion implantation process. Theintroduced impurities are activated by the heat treatment apparatus 1performing the process of heating (annealing) the semiconductor wafer Wby flash irradiation. The procedure for treatment in the heat treatmentapparatus 1 which will be described below proceeds under the control ofthe controller 3 over the operating mechanisms of the heat treatmentapparatus 1.

First, the valve 84 is opened for supply of gas, and the valves 89 and192 for exhaust of gas are opened, so that the supply and exhaust of gasinto and out of the chamber 6 start. When the valve 84 is opened,nitrogen gas is supplied through the gas supply opening 81 into the heattreatment space 65. When the valve 89 is opened, the gas within thechamber 6 is exhausted through the gas exhaust opening 86. This causesthe nitrogen gas supplied from an upper portion of the heat treatmentspace 65 in the chamber 6 to flow downwardly and then to be exhaustedfrom a lower portion of the heat treatment space 65.

The gas within the chamber 6 is exhausted also through the transportopening 66 by opening the valve 192. Further, the exhaust mechanism notshown exhausts an atmosphere near the drivers of the transfer mechanism10. It should be noted that the nitrogen gas is continuously suppliedinto the heat treatment space 65 during the heat treatment of asemiconductor wafer W in the heat treatment apparatus 1. The amount ofnitrogen gas supplied into the heat treatment space 65 is changed asappropriate in accordance with process steps.

Subsequently, the gate valve 185 is opened to open the transport opening66. A transport robot outside the heat treatment apparatus 1 transportsthe semiconductor wafer W subjected to the ion implantation through thetransport opening 66 into the heat treatment space 65 of the chamber 6.The semiconductor wafer W transported into the heat treatment space 65by the transport robot is moved forward to a position lying immediatelyover the holder 7 and is stopped thereat. Then, the pair of transferarms 11 of the transfer mechanism 10 is moved horizontally from theretracted position to the transfer operation position and is then movedupwardly, whereby the lift pins 12 pass through the through holes 79 andprotrude from the upper surface of the susceptor 74 to receive thesemiconductor wafer W.

After the semiconductor wafer W is placed on the lift pins 12, thetransport robot moves out of the heat treatment space 65, and the gatevalve 185 closes the transport opening 66. Then, the pair of transferarms 11 moves downwardly to transfer the semiconductor wafer W from thetransfer mechanism 10 to the susceptor 74 of the holder 7, so that thesemiconductor wafer W is held in a horizontal attitude. Thesemiconductor wafer W is held on the susceptor 74 in such an attitudethat the ion-implanted surface thereof is the upper surface. Also, thesemiconductor wafer W is held inside the five guide pins 76 on the uppersurface of the susceptor 74. The pair of transfer arms 11 moveddownwardly below the susceptor 74 is moved back to the retractedposition, i.e. to the inside of the recessed portion 62, by thehorizontal movement mechanism 13.

After the semiconductor wafer W is placed and held on the susceptor 74of the holder 7, the 40 halogen lamps HL in the halogen heating part 4turn on simultaneously to start preheating (or assist-heating). Halogenlight emitted from the halogen lamps HL is transmitted through the lowerchamber window 64 and the susceptor 74 both made of quartz, and impingesupon the back surface of the semiconductor wafer W. The back surface ofthe semiconductor wafer W refers to a main surface thereof on oppositeside from the front surface subjected to the ion implantation. Thesemiconductor wafer W is irradiated with the halogen light from thehalogen lamps HL, so that the temperature of the semiconductor wafer Wincreases. It should be noted that the transfer arms 11 of the transfermechanism 10, which are retracted to the inside of the recessed portion62, do not become obstacles to the heating using the halogen lamps HL.

FIG. 9 is a graph showing changes in the temperature of the frontsurface of the semiconductor wafer W. After the semiconductor wafer W istransported into the heat treatment space 65 and is placed on thesusceptor 74, the controller 3 turns on the 40 halogen lamps HL at timet0 to increase the temperature of the semiconductor wafer W irradiatedwith the halogen light to a preheating temperature T1 of 800° C. orbelow (in the present preferred embodiment, 500° C.).

The temperature of the semiconductor wafer W is measured with thecontact-type thermometer 130 when the halogen lamps HL perform thepreheating. Specifically, the contact-type thermometer 130 incorporatinga thermocouple comes through the notch 77 into contact with the lowersurface of the semiconductor wafer W held by the susceptor 74 to measurethe temperature of the semiconductor wafer W which is on the increase.The measured temperature of the semiconductor wafer W is transmitted tothe controller 3. The controller 3 controls the output from the halogenlamps HL while monitoring whether the temperature of the semiconductorwafer W which is on the increase by the irradiation with light from thehalogen lamps HL reaches the predetermined preheating temperature T1 ornot. In other words, the controller 3 exercises feedback control of theoutput from the halogen lamps HL, based on the value measured with thecontact-type thermometer 130, so that the temperature of thesemiconductor wafer W is equal to the preheating temperature T1.

After the temperature of the semiconductor wafer W reaches thepreheating temperature T1, the controller 3 maintains the temperature ofthe semiconductor wafer W at the preheating temperature T1 for a shorttime. Specifically, at time t1 when the temperature of the semiconductorwafer W measured with the contact-type thermometer 130 reaches thepreheating temperature T1, the controller 3 controls the output from thehalogen lamps HL to maintain the temperature of the semiconductor waferW at approximately the preheating temperature T1.

By performing such preheating using the halogen lamps HL, thetemperature of the entire semiconductor wafer W is uniformly increasedto the preheating temperature T1. In the stage of preheating using thehalogen lamps HL, the semiconductor wafer W shows a tendency to be lowerin temperature in a peripheral portion thereof where heat dissipation ismore liable to occur than in a central portion thereof. However, thehalogen lamps HL in the halogen heating part 4 are disposed at a higherdensity in the region opposed to the peripheral portion of thesemiconductor wafer W than in the region opposed to the central portionthereof. This causes a greater amount of light to impinge upon theperipheral portion of the semiconductor wafer W where heat dissipationis liable to occur, thereby providing a uniform in-plane temperaturedistribution of the semiconductor wafer W in the stage of preheating.Further, the inner peripheral surface of the lower reflective ring 69mounted to the chamber side portion 61 is provided as a mirror surface.Thus, a greater amount of light is reflected from the inner peripheralsurface of the lower reflective ring 69 toward the peripheral portion ofthe semiconductor wafer W. This provides a more uniform in-planetemperature distribution of the semiconductor wafer W in the stage ofpreheating.

Next, the flash lamps FL emit a flash of light to perform a flashheating treatment at time t2 when a predetermined time period haselapsed since the temperature of the semiconductor wafer W reached thepreheating temperature T1. It should be noted that a time periodrequired for the temperature of the semiconductor wafer W at roomtemperature to reach the preheating temperature T1 (a time intervalbetween the time t0 and the time t1) is only on the order of severalseconds, and that a time period required between the instant at whichthe temperature of the semiconductor wafer W reaches the preheatingtemperature T1 and the instant at which the flash lamps FL emit a flashof light (a time interval between the time t1 and the time t2) is alsoonly on the order of several seconds. For the flash irradiation fromeach flash lamp FL, the capacitor 93 is charged in advance by thecharging unit 95. Then, with the capacitor 93 in the charged state, thepulse generator 31 in the controller 3 outputs a pulse signal to theswitching element 96 to drive the switching element 96 on and off.

The waveform of the pulse signal is defined by inputting from the inputpart 33 a recipe that is a sequence of defined parameters including atime interval (ON time interval) equivalent to the pulse width and atime interval (OFF time interval) between pulses. After an operatorinputs such a recipe from the input part 33 to the controller 3, thewaveform setting part 32 in the controller 3 sets a pulse waveformhaving repeated ON and OFF time intervals in accordance with the recipe.Then, the pulse generator 31 outputs the pulse signal in accordance withthe pulse waveform set by the waveform setting part 32. As a result, thepulse signal having the set waveform is applied to the gate of theswitching element 96 to control the driving on and off of the switchingelement 96. Specifically, the switching element 96 is on when the pulsesignal inputted to the gate of the switching element 96 is on, and theswitching element 96 is off when the pulse signal is off.

In synchronism with the turning on of the pulse signal outputted fromthe pulse generator 31, the controller 3 controls the trigger circuit 97to apply a high voltage (trigger voltage) to the trigger electrode 91.The pulse signal is inputted to the gate of the switching element 96,with the electrical charges stored in the capacitor 93, and the highvoltage is applied to the trigger electrode 91 in synchronism with theturning on of the pulse signal, whereby a current flows across theelectrodes of the glass tube 92 whenever the pulse signal is on. Theresultant excitation of xenon atoms or molecules induces light emission.

The flash lamps FL emit light at the time t2 in this manner, so that thefront surface of the semiconductor wafer W held by the holder 7 isirradiated with a flash of light. If a flash lamp FL emits light withoutusing the switching element 96, the electrical charges stored in thecapacitor 93 are consumed by the single light emission, so that theoutput waveform from the flash lamp FL exhibits a single pulse having awidth on the order of 0.1 to 10 milliseconds. On the other hand, theswitching element 96 is connected in the circuit and the pulse signal isoutputted to the gate of the switching element 96 according to thepresent preferred embodiment. Thus, the switching element 96intermittently supplies the electrical charges from the capacitor 93 tothe flash lamp FL to control the current flowing to the flash lamp FL.As a result, the light emission from the flash lamp FL is accordinglychopper-controlled, which allows the electrical charges stored in thecapacitor 93 to be consumed in a divided manner. This enables the flashlamp FL to repeatedly flash on and off in an extremely short time. Itshould be noted that, before the value of the current flowing in thecircuit reaches exactly zero, the next pulse is applied to the gate ofthe switching element 96 to increase the current value again. For thisreason, the emission output never reaches exactly zero even while theflash lamp FL repeatedly flashes on and off. Thus, the switching element96 intermittently supplies the electrical charges to the flash lamp FLto freely define the waveform of current flowing to the flash lamp FL.As a result, this freely defines the light emission pattern of the flashlamp FL to freely adjust the light emission time and the light emissionintensity. The maximum light emission time of the flash lamp FL is notgreater than one second.

In the first preferred embodiment, the 30 flash lamps FL are provided inthe flash heating part 5, and the 30 switching elements 96 are providedin a one-to-one correspondence with the 30 flash lamps FL. The waveformsetting part 32 of the controller 3 individually sets the pulsewaveforms for the 30 switching elements 96, and the pulse generator 31individually outputs the pulse signals to the 30 switching elements 96.That is, the pulse signals inputted to the 30 switching elements 96 areindependent of each other. The pulse signals having the same waveformmay be inputted to the 30 switching elements 96 at the same time or thepulse signals having waveforms different from each other may be inputtedto the 30 switching elements 96. As a result, the operations of the 30switching elements 96 are individually controlled independently of eachother, so that the light emission patterns of the 30 flash lamps FL areindividually defined.

FIG. 10 is a graph showing an example of the waveform of current flowingthrough each of the flash lamps FL when the pulse signals having thesame waveform are inputted to the 30 switching elements 96 at the sametime. The operation of each switching element 96 is driven on and off inaccordance with the waveform of the pulse signal inputted to the gate ofeach switching element 96, so that the waveform of current flowingthrough a flash lamp FL corresponding to each switching element 96 isdefined. The waveform of current as shown in FIG. 10 is defined byappropriately setting the waveform of the pulse signal inputted to eachswitching element 96 (specifically, by setting the number of pulses, theON time interval of each pulse, and a time interval between pulses). Inthe example shown in FIG. 10, the currents flowing through the 30 flashlamps FL have the same waveform because the pulse signals having thesame waveform are inputted to the 30 switching elements 96 at the sametime.

FIG. 11 is a graph showing changes in the temperature of the frontsurface of the semiconductor wafer W when the current having thewaveform of FIG. 10 flows through the 30 flash lamps FL to cause lightemission from the 30 flash lamps FL. In FIG. 11, the solid line denotesthe temperature of the central portion of the front surface of thesemiconductor wafer W, and the dotted line denotes the temperature ofthe peripheral portion of the front surface of the semiconductor waferW. It should be noted that the graphs of FIGS. 10 and 11 are plottedwith a time scale of milliseconds, whereas the graph of FIG. 9 isplotted with a time scale of seconds. Thus, the changes in temperaturein FIG. 11 occur instantaneously at the time t2 of FIG. 9 (in otherwords, FIG. 11 is a graph showing the vicinity of the time t2 of FIG. 9on an enlarged scale).

The waveform of current flowing through each flash lamp FL is generallysimilar to the light emission pattern of each flash lamp FL obtainedwhen the current flows. That is, the current having the waveform asshown in FIG. 10 flows through each flash lamp FL, so that the lightemission pattern of each flash lamp FL is that as shown in FIG. 10. Thefront surface of the semiconductor wafer W is heated by flashirradiation from the flash lamps FL which emit light in such a lightemission pattern. The current having the waveform as shown in FIG. 10flows through each flash lamp FL to thereby increase the temperature ofthe front surface of the semiconductor wafer W from the preheatingtemperature T1 to a treatment temperature T2. The temperature of thefront surface of the semiconductor wafer W is maintained at thetreatment temperature T2 for a short time, and thereafter startsdecreasing from the treatment temperature T2. The treatment temperatureT2 is in the range of 1000° C. to 1200° C. where the activation of theimpurities is achieved, and shall be 1000° C. in the present preferredembodiment.

When the pulse signals having the same waveform are inputted to the 30switching elements 96 at the same time and the currents flowing throughthe 30 flash lamps FL have the same waveform, there are cases where thetemperature of the peripheral portion of the semiconductor wafer W islower than the temperature of the central portion thereof, as shown inFIG. 11. Such a nonuniform in-plane temperature distribution of thesemiconductor wafer W during the flash irradiation results in variationsin characteristics of devices such as transistors manufactured from thissemiconductor wafer W.

To overcome such a problem, the first preferred embodiment is configuredto measure the in-plane temperature distribution of the semiconductorwafer W in the case where the currents flowing through the 30 flashlamps FL have the same waveform, thereby controlling the operations ofthe 30 switching elements 96, based on the result of measurement. Also,the charging voltages applied from the charging units 95 to thecapacitors 93 are controlled, based on the result of measurement.

The control of the operations of the 30 switching elements 96 based onthe result of measurement of the in-plane temperature distribution is ofthree types to be described below. The first type of the operationcontrol is such that the controller 3 automatically sets the waveformsof the pulse signals to be outputted to the 30 switching elements 96,respectively, based on the result of measurement of the in-planetemperature distribution. Specifically, flash irradiation is performedon, for example, a test semiconductor wafer W under conditions where thecurrents flowing through the 30 flash lamps FL have the same waveform asdescribed above. The temperature of the front surface of thesemiconductor wafer W at that time is measured with the radiationthermometer 140 and the radiation thermometer 150. The radiationthermometer 140 measures the temperature of the peripheral portion ofthe semiconductor wafer W subjected to the flash heating. The radiationthermometer 150, on the other hand, measures the temperature of thecentral portion of the semiconductor wafer W subjected to the flashheating. The results of measurement with the radiation thermometer 140and the radiation thermometer 150 are stored in a storage part (a memoryor a magnetic disk) in the controller 3.

The waveform setting part 32 of the controller 3 sets the waveforms ofthe pulse signals to be outputted to the 30 switching elements 96,respectively, based on the results of measurement with the radiationthermometer 140 and the radiation thermometer 150. When the temperatureof the peripheral portion of the semiconductor wafer W is lower thanthat of the central portion thereof, as shown in FIG. 11, that is, whenthe result of measurement with the radiation thermometer 140 is lowerthan the result of measurement with the radiation thermometer 150, thesetting is made so that pulse signals to be outputted to switchingelements 96 corresponding to some of the flash lamps FL which are in thevicinity of the edge portion of the arrangement of the 30 flash lamps FLhave a relatively long ON time interval. Specifically, the waveformsetting part 32 sets the waveforms of the pulse signals to be outputtedto the respective switching elements 96 so that the ON time interval ofthe pulse signals to be outputted to the switching elements 96corresponding to some of the flash lamps FL which are in the vicinity ofthe edge portion of the arrangement of the 30 flash lamps FL is longerthan the ON time interval of pulse signals to be outputted to switchingelements 96 corresponding to some of the flash lamps FL which are in thevicinity of the central portion of the arrangement.

By inputting the pulse signals having the waveforms individually set inthis manner to the 30 switching elements 96 respectively, the currentsflowing through the 30 flash lamps FL have waveforms as shown in FIG.12. In FIG. 12, the solid line denotes the waveform of current flowingthrough the flash lamps FL lying in the vicinity of the central portionof the arrangement of the 30 flash lamps FL, and the dotted line denotesthe waveform of current flowing through the flash lamps FL lying in thevicinity of the edge portion thereof. As a result of causing thewaveforms of the pulse signals inputted to the 30 switching elements 96to differ in the aforementioned manner, the current flowing through theflash lamps FL lying in the vicinity of the edge portion of thearrangement of the 30 flash lamps FL is higher than the current flowingthrough the flash lamps FL lying in the vicinity of the central portionthereof. Accordingly, the light emission intensity of the flash lamps FLlying in the vicinity of the edge portion is higher than that of theflash lamps FL lying in the vicinity of the central portion.

FIG. 13 is a graph showing changes in the temperature of the frontsurface of the semiconductor wafer W when the current having thewaveform of FIG. 12 flows through the 30 flash lamps FL to cause lightemission from the 30 flash lamps FL. The current having the waveform asshown in FIG. 12 flows through each flash lamp FL, so that the lightemission pattern of each flash lamp FL is that as shown in FIG. 12. Itshould be noted that the light emission intensity of the flash lamps FLlying in the vicinity of the edge portion of the arrangement of the 30flash lamps FL is higher than that of the flash lamps FL lying in thevicinity of the central portion thereof. The front surface of thesemiconductor wafer W is heated by the flash irradiation from the 30flash lamps FL which emit light in such a light emission pattern. Thecurrent having the waveform as shown in FIG. 12 flows through each flashlamp FL to thereby increase the temperature of the front surface of thesemiconductor wafer W from the preheating temperature T1 to thetreatment temperature T2. The temperature of the front surface of thesemiconductor wafer W is maintained at the treatment temperature T2 fora short time, and thereafter starts decreasing from the treatmenttemperature T2.

In the example shown in FIG. 13, the light emission intensity of theflash lamps FL lying in the vicinity of the edge portion of thearrangement of the 30 flash lamps FL is higher than that of the flashlamps FL lying in the vicinity of the central portion thereof. Thisprovides a higher illuminance in the peripheral portion of thesemiconductor wafer W where a temperature decrease is prone to occur. Asa result, the in-plane temperature distribution of the semiconductorwafer W during the flash irradiation is uniform. The uniform in-planetemperature distribution of the semiconductor wafer W during the flashirradiation provides uniform characteristics of devices manufacturedfrom this semiconductor wafer W.

Next, the second type of the operation control of the switching elements96 is such that an operator of the apparatus manually sets the waveformsof the pulse signals to be outputted to the 30 switching elements 96,respectively, based on the result of measurement of the in-planetemperature distribution. In this case, flash irradiation is performedon, for example, a test semiconductor wafer W under conditions where thecurrents flowing through the 30 flash lamps FL have the same waveform,as in the case of the first type. The temperature of the front surfaceof the semiconductor wafer W at that time is measured with the radiationthermometer 140 and the radiation thermometer 150. The radiationthermometer 140 measures the temperature of the peripheral portion ofthe semiconductor wafer W subjected to the flash heating. The radiationthermometer 150, on the other hand, measures the temperature of thecentral portion of the semiconductor wafer W subjected to the flashheating. The results of measurement with the radiation thermometer 140and the radiation thermometer 150 are displayed on a display part (notshown) and the like in the heat treatment apparatus 1, for example.

The operator sets the waveforms of the pulse signals to be outputted tothe 30 switching elements 96, respectively, based on the results ofmeasurement with the radiation thermometer 140 and the radiationthermometer 150. The settings of the waveforms at this time are similarto those of the aforementioned first type. Specifically, the waveformsof the pulse signals to be outputted to the respective switchingelements 96 are set so that the ON time interval of the pulse signals tobe outputted to the switching elements 96 corresponding to the flashlamps FL lying in the vicinity of the edge portion of the arrangement ofthe 30 flash lamps FL is longer than the ON time interval of the pulsesignals to be outputted to the switching elements 96 corresponding tothe flash lamps FL lying in the vicinity of the central portion of thearrangement.

Parameters of the waveforms of the pulse signals set by the operator areinputted from the input part 33 to the controller 3. The waveformsetting part 32 sets the pulse waveforms in accordance with the inputsto thereby cause the currents having the waveforms of FIG. 12 to flowthrough the 30 flash lamps FL, as in the case of the first type. Thisachieves the uniform in-plane temperature distribution of thesemiconductor wafer W during the flash irradiation.

The third type of the operation control of the switching elements 96 issuch that the controller 3 exercises feedback control of the 30switching elements 96 in real time, based on the result of measurementof the in-plane temperature distribution. In this case, while the flashirradiation from the 30 flash lamps FL is performed on the semiconductorwafer W to be treated, the temperature of the front surface of thesemiconductor wafer W at that time is measured with the radiationthermometer 140 and the radiation thermometer 150. The radiationthermometer 140 measures the temperature of the peripheral portion ofthe semiconductor wafer W subjected to the flash heating. The radiationthermometer 150, on the other hand, measures the temperature of thecentral portion of the semiconductor wafer W subjected to the flashheating. The results of measurement with the radiation thermometer 140and the radiation thermometer 150 are transmitted to the controller 3.

The controller 3 makes a correction to the waveforms of the pulsesignals being outputted to the 30 switching elements 96, respectively,based on the results of measurement with the radiation thermometer 140and the radiation thermometer 150. When the temperature of theperipheral portion of the semiconductor wafer W is lower than thetemperature of the central portion thereof, the controller 3 makes acorrection to the waveforms of the pulse signals so that the pulsesignals being outputted to the switching elements 96 corresponding tothe flash lamps FL lying in the vicinity of the edge portion of thearrangement of the 30 flash lamps FL have a relatively long ON timeinterval. Specifically, the ON time interval of the pulse signals beingoutputted to the switching elements 96 corresponding to the flash lampsFL lying in the vicinity of the edge portion of the arrangement of the30 flash lamps FL is made longer or the ON time interval of the pulsesignals being outputted to the switching elements 96 corresponding tothe flash lamps FL lying in the vicinity of the central portion of thearrangement is made shorter.

Thus, the currents flowing through the flash lamps FL lying in thevicinity of the edge portion of the arrangement of the 30 flash lamps FLis made relatively higher than the currents flowing through the flashlamps FL lying in the vicinity of the central portion thereof.Accordingly, the light emission intensity of the flash lamps FL lying inthe vicinity of the edge portion is higher than that of the flash lampsFL lying in the vicinity of the central portion. As a result, thisprovides a higher illuminance of a flash of light in the peripheralportion of the semiconductor wafer W where a temperature decrease hasoccurred to achieve the uniform in-plane temperature distribution of thesemiconductor wafer W during the flash irradiation.

In the case of the third type, it can be supposed that the computationprocess cannot follow the aforementioned correction process, dependingon the processing speed of the controller 3, because the time period forthe light emission from the flash lamps FL is extremely short (notgreater than one second, and in general several to tens of millimeters).In such a case, a plurality of patterns of the waveforms of the pulsesignals to be outputted to the switching elements 96 are previouslyprepared and stored in the storage part of the controller 3. It isdesirable that waveform patterns for temperature increase, waveformpatterns for temperature maintenance and the like are prepared. Thecontroller 3 may select an optimum waveform from the plurality ofprepared patterns of the waveforms of the pulse signals, based on theresults of measurement with the radiation thermometer 140 and theradiation thermometer 150. This enables the controller 3 to exercise thefeedback control of the 30 switching elements 96 in real time in ashorter computation processing time.

In the first preferred embodiment, the controller 3 controls thecharging voltages applied from the charging units 95 to the capacitors93, respectively, based on the result of measurement of the in-planetemperature distribution of the semiconductor wafer W. The control ofthe charging voltages is of two types to be described below. The firsttype of the control of the charging voltages is such that the controller3 automatically sets the charging voltages to the 30 capacitors 93,respectively, based on the result of measurement of the in-planetemperature distribution. In the aforementioned manner, flashirradiation is performed on, for example, a test semiconductor wafer Wunder conditions where the currents flowing through the 30 flash lampsFL have the same waveform. The temperature of the front surface of thesemiconductor wafer W at that time is measured with the radiationthermometer 140 and the radiation thermometer 150. The radiationthermometer 140 measures the temperature of the peripheral portion ofthe semiconductor wafer W subjected to the flash heating. The radiationthermometer 150, on the other hand, measures the temperature of thecentral portion of the semiconductor wafer W subjected to the flashheating. The results of measurement with the radiation thermometer 140and the radiation thermometer 150 are stored in the storage part in thecontroller 3.

The controller 3 sets the charging voltages to the 30 capacitors 93,respectively, based on the results of measurement with the radiationthermometer 140 and the radiation thermometer 150. When the temperatureof the peripheral portion of the semiconductor wafer W is lower than thetemperature of the central portion thereof, as shown in FIG. 11, thatis, when the result of measurement with the radiation thermometer 140 islower than the result of measurement with the radiation thermometer 150,the setting is made so that charging voltages to capacitors 93corresponding to the flash lamps FL lying in the vicinity of the edgeportion of the arrangement of the 30 flash lamps FL are relatively high.Specifically, the controller 3 sets the charging voltages to therespective capacitors 93 so that the charging voltages to the capacitors93 corresponding to the flash lamps FL lying in the vicinity of the edgeportion of the arrangement of the 30 flash lamps FL are higher thancharging voltages to capacitors 93 corresponding to the flash lamps FLlying in the vicinity of the central portion of the arrangement.

The controller 3 controls the 30 charging units 95 so that the chargingvoltages individually set in this manner are used to charge the 30capacitors 93. As a result of causing the charging voltages to the 30capacitors 93 to differ in the aforementioned manner, the light emissionintensity of the flash lamps FL lying in the vicinity of the edgeportion of the arrangement of the 30 flash lamps FL is higher than thatof the flash lamps FL lying in the vicinity of the central portion. As aresult, this provides a higher illuminance of a flash of light in theperipheral portion of the semiconductor wafer W where a temperaturedecrease is prone to occur to achieve the uniform in-plane temperaturedistribution of the semiconductor wafer W during the flash irradiation.

The second type of the control of the charging voltages is such that anoperator of the apparatus manually sets the charging voltages appliedfrom the charging units 95 to the capacitors 93, respectively, based onthe result of measurement of the in-plane temperature distribution. Inthis case, flash irradiation is performed on, for example, a testsemiconductor wafer W under conditions where the currents flowingthrough the 30 flash lamps FL have the same waveform as described above,as in the case of the first type. The temperature of the front surfaceof the semiconductor wafer W at that time is measured with the radiationthermometer 140 and the radiation thermometer 150. The radiationthermometer 140 measures the temperature of the peripheral portion ofthe semiconductor wafer W subjected to the flash heating. The radiationthermometer 150, on the other hand, measures the temperature of thecentral portion of the semiconductor wafer W subjected to the flashheating. The results of measurement with the radiation thermometer 140and the radiation thermometer 150 are displayed on the display part andthe like in the heat treatment apparatus 1, for example.

The operator sets the charging voltages to the 30 capacitors 93,respectively, based on the results of measurement with the radiationthermometer 140 and the radiation thermometer 150. The settings of thevoltages at this time are similar to those of the aforementioned firsttype. Specifically, the operator sets the charging voltages to therespective capacitors 93 so that the charging voltages to the capacitors93 corresponding to the flash lamps FL lying in the vicinity of the edgeportion of the arrangement of the 30 flash lamps FL are higher than thecharging voltages to the capacitors 93 corresponding to the flash lampsFL lying in the vicinity of the central portion of the arrangement.

The set values of the charging voltages set by the operator are inputtedfrom the input part 33 to the controller 3. The controller 3 controlsthe charging units 95 to charge the capacitors 93 in accordance with theinputs, whereby the light emission intensity of the flash lamps FL lyingin the vicinity of the edge portion of the arrangement of the 30 flashlamps FL is higher than that of the flash lamps FL lying in the vicinityof the central portion. As a result, this provides a higher illuminanceof a flash of light in the peripheral portion of the semiconductor waferW where a temperature decrease is prone to occur to achieve the uniformin-plane temperature distribution of the semiconductor wafer W duringthe flash irradiation.

In the first preferred embodiment as described above, the 30 switchingelements 96 are provided in a one-to-one correspondence with the 30flash lamps FL, and the controller 3 individually controls theoperations of the 30 switching elements 96 to individually define thelight emission patterns of the 30 flash lamps FL. In the first preferredembodiment, the radiation thermometer 140 and the radiation thermometer150 are provided to measure the in-plane temperature distribution of thesemiconductor wafer W, and the controller 3 individually controls theoperations of the 30 switching elements 96, based on the results ofmeasurement with the radiation thermometer 140 and the radiationthermometer 150. Also, the controller 3 individually controls thecharging voltages applied from the charging units 95 to the capacitors93, based on the results of measurement with the radiation thermometer140 and the radiation thermometer 150. The individual control of thelight emission patterns of the plurality of flash lamps FL and thecharging voltages to the plurality of capacitors 93 corresponding to theplurality of flash lamps FL makes the illuminance of a flash of lightrelatively high in a region of the semiconductor wafer W where atemperature decrease is prone to occur to achieve the uniform in-planetemperature distribution of the semiconductor wafer W during the flashirradiation.

Referring again to FIG. 9, the halogen lamps HL turn off at time t3which is a predetermined time period later than the time at which theflash irradiation is completed and the light emission from the flashlamps FL is stopped. This causes the temperature of the semiconductorwafer W to start decreasing from the preheating temperature T1. Afterthe temperature of the semiconductor wafer W is decreased to thepredetermined temperature or below, the pair of transfer arms 11 of thetransfer mechanism 10 is moved horizontally again from the retractedposition to the transfer operation position and is then moved upwardly,whereby the lift pins 12 protrude from the upper surface of thesusceptor 74 to receive the heat-treated semiconductor wafer W from thesusceptor 74. Subsequently, the transport opening 66 which has beenclosed is opened by the gate valve 185, and the transport robot outsidethe heat treatment apparatus 1 transports the semiconductor wafer Wplaced on the lift pins 12 to the outside. Thus, the heat treatmentapparatus 1 completes the heating treatment of the semiconductor waferW.

Second Preferred Embodiment

Next, a second preferred embodiment according to the present inventionwill be described. A heat treatment apparatus according to the secondpreferred embodiment is exactly identical in configuration with thataccording to the first preferred embodiment. A procedure for thetreatment of a semiconductor wafer W according to the second preferredembodiment is generally similar to that according to the first preferredembodiment. The operations of the switching elements 96 and the chargingvoltages to the capacitors 93 are controlled in the first preferredembodiment, based on the result of measurement of the in-planetemperature distribution of the semiconductor wafer W. In the secondpreferred embodiment, similar control is exercised based on the resultof measurement of an illuminance distribution of the arrangement of the30 flash lamps FL. Specifically, the controller 3 controls theoperations of the 30 switching elements 96 and the charging voltagesapplied from the charging units 95 to the capacitors 93, based on theresults of measurement with the illuminance sensor 240 and theilluminance sensor 250.

As in the first preferred embodiment, the control of the operations ofthe 30 switching elements 96 based on the result of measurement of theilluminance distribution is of three types to be described below. Thefirst type of the operation control is such that the controller 3automatically sets the waveforms of the pulse signals to be outputted tothe 30 switching elements 96, respectively, based on the result ofmeasurement of the illuminance distribution. The illuminance of thearrangement of the flash lamps FL is measured with the illuminancesensor 240 and the illuminance sensor 250 when a flash of light isemitted from the 30 flash lamps FL. The illuminance sensor 240 measuresthe illuminance in the vicinity of the edge portion of the arrangementof the 30 flash lamps FL. The illuminance sensor 250, on the other hand,measures the illuminance in the vicinity of the central portion of thearrangement of the 30 flash lamps FL.

The waveform setting part 32 of the controller 3 sets the waveforms ofthe pulse signals to be outputted to the 30 switching elements 96,respectively, based on the results of measurement with the illuminancesensor 240 and the illuminance sensor 250. When the illuminance in thecentral portion of the arrangement of the 30 flash lamps FL is lowerthan the illuminance in the edge portion thereof, that is, when theresult of measurement with the illuminance sensor 250 is lower than theresult of measurement with the illuminance sensor 240, the setting ismade so that the pulse signals to be outputted to the switching elements96 corresponding to the flash lamps FL lying in the vicinity of thecentral portion of the arrangement of the 30 flash lamps FL have arelatively long ON time interval. Specifically, the waveform settingpart 32 sets the waveforms of the pulse signals to be outputted to therespective switching elements 96 so that the ON time interval of thepulse signals to be outputted to the switching elements 96 correspondingto the flash lamps FL lying in the vicinity of the central portion ofthe arrangement of the 30 flash lamps FL is longer than the ON timeinterval of the pulse signals to be outputted to the switching elements96 corresponding to the flash lamps FL lying in the vicinity of the edgeportion of the arrangement.

This provides a uniform illuminance distribution at the surface of thearrangement of the 30 flash lamps FL to consequently achieve the uniformin-plane temperature distribution of the semiconductor wafer W duringthe flash irradiation.

The second type of the operation control of the switching elements 96 issuch that an operator of the apparatus manually sets the waveforms ofthe pulse signals to be outputted to the 30 switching elements 96,respectively, based on the result of measurement of the illuminancedistribution. In place of the controller 3, the operator sets thewaveforms of the pulse signals, based on the result of measurement ofthe illuminance distribution, as in the case of the second type of theoperation control of the switching elements 96 in the first preferredembodiment. The settings of the waveforms at this time are similar tothose of the aforementioned first type.

The third type of the operation control of the switching elements 96 issuch that the controller 3 exercises feedback control of the 30switching elements 96 in real time, based on the result of measurementof the illuminance distribution. The controller 3 makes a correction tothe waveforms of the pulse signals being outputted to the 30 switchingelements 96, respectively, based on the results of measurement with theilluminance sensor 240 and the illuminance sensor 250, as in the case ofthe third type of the operation control of the switching elements 96 inthe first preferred embodiment. For example, when the illuminance in thecentral portion of the arrangement of the 30 flash lamps FL is lowerthan the illuminance in the edge portion thereof, the controller 3 makesa correction to the waveforms of the pulse signals so that pulse signalsbeing outputted to the switching elements 96 corresponding to the flashlamps FL lying in the vicinity of the central portion of the arrangementof the 30 flash lamps FL have a relatively long ON time interval. Thisprovides a uniform illuminance distribution at the surface of thearrangement of the 30 flash lamps FL to consequently achieve the uniformin-plane temperature distribution of the semiconductor wafer W duringthe flash irradiation.

In the second preferred embodiment, the controller 3 controls thecharging voltages applied from the charging units 95 to the capacitors93, respectively, based on the result of measurement of the illuminancedistribution of the arrangement of the 30 flash lamps FL. As in thefirst preferred embodiment, the control of the charging voltages is oftwo types to be described below. The first type of the control of thecharging voltages is such that the controller 3 automatically sets thecharging voltages to the 30 capacitors 93, respectively, based on theresult of measurement of the illuminance distribution. In theaforementioned manner, the illuminance of the arrangement of the flashlamps FL is measured with the illuminance sensor 240 and the illuminancesensor 250 when a flash of light is emitted from the 30 flash lamps FL.

The controller 3 sets the charging voltages to the 30 capacitors 93,respectively, based on the results of measurement with the illuminancesensor 240 and the illuminance sensor 250. When the result ofmeasurement with the illuminance sensor 240 is lower than the result ofmeasurement with the illuminance sensor 250, the setting is made so thatthe charging voltages to the capacitors 93 corresponding to the flashlamps FL lying in the vicinity of the edge portion of the arrangement ofthe 30 flash lamps FL are relatively high. Specifically, the controller3 sets the charging voltages to the capacitors 93 so that the chargingvoltages to the capacitors 93 corresponding to the flash lamps FL lyingin the vicinity of the edge portion of the arrangement of the 30 flashlamps FL are higher than the charging voltages to capacitors 93corresponding to the flash lamps FL lying in the vicinity of the centralportion of the arrangement.

The controller 3 controls the 30 charging units 95 so that the chargingvoltages individually set in this manner are used to charge the 30capacitors 93. As a result of causing the charging voltages to the 30capacitors 93 to differ in the aforementioned manner, the illuminancedistribution at the surface of the arrangement of the 30 flash lamps FLis uniform. This achieves the uniform in-plane temperature distributionof the semiconductor wafer W during the flash irradiation.

The second type of the control of the charging voltages is such that anoperator of the apparatus manually sets the charging voltages appliedfrom the charging units 95 to the capacitors 93, respectively, based onthe result of measurement of the illuminance distribution. In place ofthe controller 3, the operator sets the charging voltages to the 30capacitors 93, based on the result of measurement of the illuminancedistribution, as in the case of the second type of the control of thecharging voltages in the first preferred embodiment. The settings of thevoltages are similar to those of the aforementioned first type.

In the second preferred embodiment as described above, the 30 switchingelements 96 are provided in a one-to-one correspondence with the 30flash lamps, and the controller 3 individually controls the operationsof the 30 switching elements 96 to individually define the lightemission patterns of the 30 flash lamps FL. In the second preferredembodiment, the illuminance sensor 240 and the illuminance sensor 250are provided to measure the illuminance distribution of the arrangementof the 30 flash lamps FL, and the controller 3 individually controls theoperations of the 30 switching elements 96, based on the results ofmeasurement with the illuminance sensor 240 and the illuminance sensor250. Also, the controller 3 individually controls the charging voltagesapplied from the charging units 95 to the capacitors 93, based on theresults of measurement with the illuminance sensor 240 and theilluminance sensor 250. The individual control of the light emissionpatterns of the plurality of flash lamps FL and the charging voltages tothe plurality of capacitors 93 corresponding to the plurality of flashlamps FL makes the illuminance distribution at the surface of thearrangement of the flash lamps FL uniform. As a result, this achievesthe uniform in-plane temperature distribution of the semiconductor waferW during the flash irradiation.

<Modifications>

While the preferred embodiments according to the present invention havebeen described hereinabove, various modifications of the presentinvention in addition to those described above may be made withoutdeparting from the scope and spirit of the invention. For example, thecontroller 3 individually controls the operations of the 30 switchingelements 96 to individually define the light emission patterns of the 30flash lamps FL in the aforementioned preferred embodiments. However, the30 flash lamps FL may be divided into a plurality of lamp groups, sothat control is exercised on a zone-by-zone basis.

FIG. 14 is a view showing an example of the 30 flash lamps FL dividedinto a plurality of flash lamp groups. In the example of FIG. 14, the 30flash lamps FL are divided into five flash lamp groups. Specifically,the arrangement of the 30 flash lamps FL is divided into five: a flashlamp group FG3 in a central zone, flash lamp groups FG1 and FG5 inopposite end zones, and flash lamp groups FG2 and FG4 in intermediatezones between the central and opposite end zones. Each of the five flashlamp groups FG1, FG2, FG3, FG4 and FG5 includes six flash lamps FL. Thecontroller 3 outputs pulse signals having the same waveform at the sametime to six switching elements 96 corresponding to the six flash lampsFL included in each of the five flash lamp groups FG1, FG2, FG3, FG4 andFG5. Thus, the six flash lamps FL included in each flash lamp group havethe same light emission pattern. This allows the controller 3 to controlthe operation of the switching elements 96 for each flash lamp group,thereby defining the light emission pattern for each flash lamp group.

On the other hand, the controller 3 in the first and second preferredembodiments individually controls the operations of the 30 switchingelements 96 to individually define the light emission patterns of the 30flash lamps FL. Thus, the pulse signals having different pulse waveformsmay be outputted to all of the 30 switching elements 96, so that all ofthe 30 flash lamps FL have different light emission patterns.

In summary, the controller 3 is required only to individually controlthe operations of the 30 switching elements 96 so that some of the flashlamps FL corresponding to a region of the semiconductor wafer W where atemperature decrease occurs during flash irradiation or a region of thearrangement of the flash lamps FL where an illuminance decrease occurshave a relatively high illuminance.

In the first and second preferred embodiments, the controller 3 controlsboth the operations of the 30 switching elements 96 and the chargingvoltages applied from the charging units 95 to the capacitors 93.However, the controller 3 may control only either the operations of the30 switching elements 96 or the charging voltages. Changing the chargingvoltages causes changes in the shapes of the waveforms of currentsflowing through the flash lamps FL to result in difficulties incontrolling the light emission patterns of the flash lamps FL. It ishence preferable that the controller 3 exercises at least the individualoperation control of the 30 switching elements 96.

Also, in the aforementioned preferred embodiments, the semiconductorwafer W is preheated by irradiating the semiconductor wafer W withhalogen light from the halogen lamps HL. The technique for preheating isnot limited to this, but the semiconductor wafer W may be preheated byplacing the semiconductor wafer W on a hot plate.

Further, although the voltage is applied to the trigger electrode 91 insynchronism with the turning on of the pulse signal in theaforementioned preferred embodiments, the timing of the application ofthe trigger voltage is not limited to this. The trigger voltage may beapplied at fixed time intervals independently of the waveform of thepulse signal. In a case where the pulse signal is short in timeintervals or where the passage of current is started by a pulse whilethe value of the current caused to flow through the flash lamp FL by thepreceding pulse is not less than a predetermined value, the currentcontinues to flow through the flash lamp FL without interruption. Insuch a case, it is not necessary to apply the trigger voltage for eachpulse. In other words, the timing of the application of the triggervoltage may be arbitrarily determined as long as the timing of thecurrent flow through the flash lamp FL coincides with the turning on ofthe pulse signal.

Although an IGBT is used as each of the switching elements 96 in theaforementioned preferred embodiments, another transistor capable ofturning on and off the circuit in accordance with the signal levelinputted to the gate thereof may be used in place of the IGBT. It is,however, preferable to use an IGBT and a GTO (gate turn-off) thyristorwhich are suitable for handling high power as each of the switchingelements 96 because the emission of light from the flash lamps FLconsumes considerably high power.

Although the 30 flash lamps FL are provided in the flash heating part 5according to the aforementioned preferred embodiments, the presentinvention is not limited to this. Any number of flash lamps FL may beprovided. The flash lamps FL are not limited to the xenon flash lamps,but may be krypton flash lamps. Also, the number of halogen lamps HLprovided in the halogen heating part 4 is not limited to 40. Any numberof halogen lamps HL may be provided.

Moreover, a substrate to be treated by the heat treatment apparatusaccording to the present invention is not limited to a semiconductorwafer, but may be a glass substrate for use in a flat panel display fora liquid crystal display apparatus and the like, and a substrate for asolar cell.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

What is claimed is:
 1. A method of heating a substrate by irradiatingthe substrate with a flash of light, the method comprising the step ofadjusting the ON time interval of a pulse signal to be outputted to eachof a plurality of switching elements provided in a one-to-onecorrespondence with a plurality of flash lamps for emitting a flash oflight and each defining the waveform of current flowing through acorresponding one of said flash lamps, to individually control theoperations of the switching elements and individually define the lightemission patterns of said flash lamps, wherein said flash lamps aredivided into a plurality of flash lamp groups, and wherein the lightemission pattern for each of said flash lamp groups are defined, and theON time interval of a pulse signal is set to be relatively longer, thepulse signal being outputted to each of said switching elementscorresponding to each of said flash lamp groups in an edge portion ofthe arrangement of said flash lamps out of said flash lamp groups, sothat the light emission intensity of the flash lamp groups in the edgeportion of the arrangement is higher than that of the flash lamp groupsin the central portion thereof.
 2. The method according to claim 1,including controlling operations of said switching elements, based onresults of measurement of temperatures of different regions,respectively, of a front surface of a substrate irradiated with a flashof light.
 3. The method according to claim 2, including individuallycontrolling charging voltages to a plurality of capacitors provided in aone-to-one correspondence with said flash lamps and each supplyingelectrical charge to a corresponding one of said flash lamps, based onsaid results of measurement of the temperatures.